Moment tensor inversion of recent small to moderate sized earthquakes: implications for seismic hazard and active tectonics beneath the Sea of Marmara

Abstract

SUMMARY We retrieve the moment tensors of 64 small to moderate sized events that occurred mostly beneath the Sea of Marmara using near-field data recorded at strong-motion and broad-band seismic stations. The near-field displacement records are inverted to their sources utilizing Kuge’s method where the best fit between the synthetic and observed seismograms is achieved through searching a centroid moment tensor (CMT) point in a grid scheme. We also analyse the stress fields acting in the eastern and western parts of the Sea of Marmara by inverting the P- and T-axes of the focal mechanisms obtained. Significant biases in the stress tensors are obtained. The nearly horizontal maximum compressive axis σ 1 in the western part is rotated 16 ◦ counter-clockwise compared with σ 1 in the eastern part. The σ 2-axis is close to vertical (shear tectonic regime) in the east and the plunge of σ 2-axis in the west is 36 ◦ (transpressive tectonic regime). Changes in the σ 3-axis are also observed, that is, it is close to horizontal in the east and dips 49 ◦ in the west. The spatial distribution of the focal mechanisms suggests that the stress field in the eastern part of the Sea of Marmara is homogenous compared with the western part, and we identify five distinct subsidiary faults. (1) a WNW‐ESE-striking, right-lateral strike-slip fault located a few kilometres SW of the Princes’ Islands, (2) a WSW‐ENE-striking, right-lateral strike-slip fault named the Yalova‐Hersek fault, (3) an E‐W-striking normal fault located onshore between